At the present time, optical lenses are typically generated in a wet grinding operation. Conventional lens generators include a lens holder and a revolvable oscillating grinding tool positioned in a substantially closed chamber where the grinding or cutting operation occurs. The grinding tool not only revolves as it engages the stationary lens blank, but the grinding tool also moves in an arc of a variable radius and is adjustable to change the angle of attack with respect to the lens blank. With this arrangement, the grinding tool is capable of creating a horizontal curve with one radius and a vertical curve with a different radius.
A liquid coolant, such as mineral seal oil or water containing soluble additives, is constantly sprayed on the lens blank and the grinding tool during the grinding operation. The liquid coolant is used to reduce the temperature generated during the grinding operation, and to remove the swarf material removed from the lens blank. Excessive heat produced during the grinding operation can warp the surface of the lens. The grinding tool in conventional lens generators comprises a cuplike diamond wheel which cuts the media or swarf from the surface of the lens blank.
It has been found that, even though a liquid coolant is applied to the lens blank and the grinding tool during the grinding operation, warpage from heat still occurs. In this regard, it has been found that the coolant interacts with the swarf being removed to form a mulch that tends to keep the swarf material trapped against the diamond wheel and the surface of the lens blank during the grinding operation. This trapping of the swarf-laden coolant produces the heat during the grinding operation.
The same conventional lens generators have been used to generate plastic lenses from CR-39 and polycarbonate, but supercooled coolants and various swarf separating devices have helped very little in eliminating warpage in this kind of operation. It will also be appreciated that, even though the grinding operation takes place in a substantially closed chamber, operators are constantly sprayed by the swarf-laden coolant, and the same coolant fouls the various components of the lens generator. The swarf-laden coolant in the wet grinding operation also constitutes a waste material which is difficult to dispose of.